1. Field of the Invention
The field of this invention lies within the printer and motor art. More particularly, it lies within the art of dot matrix printing wherein numerous dots are printed on a print media such as a sheet of paper to provide for an alpha numeric representation thereon. It also resides in the field of motor controls for brushless D.C. motors, D.C. brush motors and D.C. stepping motors. It specifically can relate to the field wherein line printers are driven by motors for movement across a print media in order to impress a number of dots thereon as the printer moves reciprocally across the print media. It also includes motor drives and controls for the various motors used with or analogous to the foregoing mentioned motors.
2. Prior Art and Improvements Thereover
The prior art with regard to dot matrix printers encompasses multiple printers of various configurations. Such configurations use various wheels and hammers of various types to impress a dot on a print media. One particular type of printer which is known in the art is a line printer.
Line printers generally have a series of hammers. The series of hammers are implaced on a hammerbank which reciprocally moves across a print media. The print media is advanced across the hammers and is printed thereon by an inked ribbon.
Such hammers are supported on a hammerbank. The hammers are often held in place by a permanent magnet until released or fired. The release or firing takes place by the permanent magnetism holding the print hammers being overcome.
In the past, it has been known to place a drive motor at a location to drive the hammerbank reciprocally by a crank or a connector. The crank or connector moves the hammerbank in a reciprocal manner in a sufficiently rapid manner so as to provide high speed printing.
A problem of the prior art is that the motor was not always consistently driven to provide for smooth and effective printing movement. The motors were driven in a buck mode, or a push pull mode, which was not always desirable.
A drawback of the prior art with regard to motor drives for both printers and various motors is that they were driven in either a buck drive mode or a push pull mode.
The buck drive had a low ripple current which improved efficiency. However, it could not decrease output current on demand. This made it very difficult for use with linear controls in order to cause the motor to function in a manner where demands were made of the type in printers and certain other motor uses.
The push pull motor drives create and decrease current on demand. Nevertheless, they suffer from high ripple current hence there is less efficiency. The push pull convertor drives the motor positively until a reference is reached. The bridge driving the motor is then reversed and the current is driven negatively until the next cycle beings. The deceleration or reduction of current in a push pull design is linear and controlled. However, it has extremely high ripple currents and it also dumps excess motor energy back to the supply. This requires extra circuits in the power system to dissipate the stored energy in the motor.
It is an object of this invention to provide a balanced buck drive. This fundamentally operates like two convertors complimenting each other.
The object is to provide this balanced buck so that the first part of the cycle drives until a positive reference is reached. Thereafter, as driven through the second part of the cycle and decreasing the current with back emf, the system continues through a third intermediate cycle and a fourth cycle making an improved balanced buck.
The balanced buck drive provides an object of this invention by maintaining a current comparable to the buck style drive. However, it is responsive to requests for more or less current within each switching cycle.
A further object to the invention is that the balanced buck drive of this motor control dissipates excess motor energy in the motor windings and not in the power system or control circuits.
Another object is that the balanced buck drive provides for more consistent printing by having smoother motor operation and a limitation of ripple currents that affect motor operation and attendant print quality.
The balanced buck drive of this invention enhances the drive of a printer motor, as well as motors in general such as brushless D.C. motors of the printer of this invention, D.C. brush motors, and D.C. stepping motors.
The objects of this invention are not only to drive the printer of this invention but also to broadly apply the applicable principles and invention hereof to other types of motors.
Another object of this invention which is significant is that the motor, counterbalance and hammerbank are keyed or linked for operation after being placed in a closed loop relationship. This effectively allows an electrically locked position between the motor and the hammerbank. This is effectuated by means of a single sensor that merely senses the position of the rotor of the motor that is in turn keyed to the position of the hammerbank.
For these reasons, the invention is a substantial step over the prior art and enhances line printer functions as well as smoothness of operation, speed of operation, and provides longevity and finer printing for a line printer than had previously been capable in the art. It also provides enhanced control of brushless D.C. motors, D.C. brush motors and D.C. stepper motors in general.